Submitted on June 5, 2006
Accepted on March 13, 2007
Significant contribution of liver non-parenchymal cells to metabolism of ammonia and lactate, and cocultivation augments the functions of a bioartificial liver
Geir Ivar Nedredal1*, Kjetil Elvevold2, Lars Marius Ytrebo3, Ole-Martin Fuskevag4, Ingvild Pettersen2, Kjell Bertheussen5, Bodil Langbakk6, Bard Smedsrod7, and Arthur Revhaug8
1 Dept of Digestive Surgery, University Hospital Northern Norway, Breivika, Tromso, 9037, Norway; Surgical Research Laboratory, University of Tromso, Tromso, Norway
2 Dept of Experimental Pathology, University of Tromso, Norway
3 Anaestesiology and Intensive Care, University Hospital Northern Norway, Sykehusveien 10, Tromsø, 9038, Norway; Surgical Research Laboratory, University of Tromso, Tromso, Norway
4 Dept of Pharmacology, University of Tromso, Tromso, Norway
5 Dept of Obstetrics and Gynecology, University Hospital Northern Norway, Tromso, Norway
6 Dept of Clinical Chemistry, University Hospital Northern Norway, Tromso, Norway
7 Dept of Experimental Pathology, University of Tromso, Tromso, Norway
8 Department of Digestive Surgery, University Hospital Northern Norway and University of Tromsø, Norway
* To whom correspondence should be addressed. E-mail: geir.ivar.nedredal{at}fagmed.uit.no.
A bioartificial liver (BAL) will bridge patients with acute liver failure (ALF) either to spontaneous regeneration or to liver transplantation. The nitrogen metabolism is important in ALF, and the metabolism of non-parenchymal liver cells (NPCs) is poorly understood. The scope of this study was to investigate whether cocultivation of hepatocytes with NPCs will augment the functions of a BAL (HN-BAL) compared to a BAL equipped with only hepatocytes (H-BAL). In addition, NPCs were similarly cultivated alone. The cells were cultivated for 8 days in simulated microgravity with serum-free growth medium.
With NPCs, initial ammonia and lactate production were fivefold and over twofold higher compared to later time periods despite sufficient oxygen supply. Initial lactate production and glutamine consumption were threefold higher in HN-BAL than in H-BAL. With NPCs, initial glutamine consumption was two-threefold higher compared to later time periods, whereas initial ornithine production and arginine consumption were over fourfold and eightfold higher compared to later time periods. In NPCs, the conversion of glutamine to glutamate and ammonia can be explained by the presence of glutaminase, as revealed by PCR analysis. Drug metabolism and clearance of aggregated gamma globulin, probes administered to test functions of hepatocytes and NPCs respectively, were higher in HN-BAL than in H-BAL.
In conclusion, NPCs produce ammonia by hydrolysis of amino acids and may contribute to the pathogenesis of ALF. High amounts of lactate are produced by NPCs under non-hypoxic conditions. Cocultivation augments differentiated functions such as drug metabolism and clearance of aggregated gamma globulin.
